This invention relates to accoustic ranging systems for cameras and more particularly, it concerns a ranging system module adapted for attachment as a unit to an existing camera with minimal modification to camera construction.
In a commonly assigned co-pending application Ser. No. 729,289, filed Oct. 4, 1976, in the name of Edwin K. Shenk, there is disclosed a camera lens focusing mechanism in which a sonic pulse generated by a camera mounted transducer is reflected from a subject to be photographed and received by the transducer to provide a range signal related to camera-subject distance. An electronic logic circuit responds to the range signal to produce a train of pulses, the number of which is representative of the lens mount axial position at which the subject will be in focus. Such pulses are gated into a counter and used for operating a drive motor coupled mechanically to the lens mount. An encoder wheel coupled rotatably with the lens mount operates as a component of an auxiliary pulse generator in a feedback system so that rotation of the drive motor under the control of the counter causes the auxiliary pulse generator to produce a predetermined number of pulses for each axial unit displacement of the lens mount. The logic circuit further responds to the output of the auxiliary pulse generator to determine when the lens mount has been moved to the position determined by the pulse train counter to be proper for focusing the subject to be photographed. Such further logic circuitry response results in a pawl engaging a lens mount coupled rack to stop movement of the lens mount at the proper focusing position even though the drive motor may continue to rotate. A slip clutch in the drive train between the motor and the lens mount facilitates this latter operating characteristic.
Such ranging systems involve as assembly of electronic, electrical and mechanical components which must be capable of smooth, precise operation in the assembly as well as accurate calibration with the lens focusing components of the camera with which the system is used.
These requirements coupled with the desirable attainment of low cost manufacture necessitate a ranging system or module capable of being pre-tested prior to assembly of the ranging system module with a camera. In addition, the physical interconnection of the ranging module with the camera must accomodate the basic camera design. In this latter respect, particular difficulty is encountered where the camera is foldable in a manner such that the lens and lens housing is adjustable between a collapsed storage condition and an erect operative condition.